It is well known that the provision of endo-extracorporeal implants in tissue of the human body involves many problems, apart from questions of rejection which are engendered whenever a foreign body is introduced into an organism. The problems increase when this body is not only in contact with tissues of the organism in which the implant is provided but is also in contact with the external milieu.
For example, where the implant traverses the tissue or emerges therefrom into the external milieu, sites are provided which can allow or encourage the entry of bacteria, the bacterial action at the regions surrounding the implant causing a progressive epithelial invagination along the implant so that the implant becomes progressively separated from healthy tissue around it.
This problem has been recognized in the past and it has been proposed to provide bacterial barriers or seals around the implant which are intended to prevent just this type of isolation of the implant by the action of microorganisms.
In U.S. Pat. No. 3,663,965, for example, a percutaneous device is described which is designed to permit the passage of a wire or tube through the skin. In this case, a sealing barrier is provided against bacterial incursion from Teflon, silicone, rubber, polypropylene, polyurethane, an epoxy or by various forms of pyrolyzed carbon.
Such systems have not been found to be fully effective and the epithelial invagination may occur in any event around the barrier which is provided. The entire structure is retained only by virtue of epithelial colonization which gives rise to microscopic perforations of the support. The perforations tend to slow the development of bacteria in the space between the epithelium and the foreign body, a space which cannot be cleansed free from the bacteria in any practical manner.
The European patent No. EP-A 0,039,189 describes a hypodermic apparatus which comprises a pin whose upper portion is formed with a knob, which, like the lower knob, is constituted of expanded polytetrafluoroethylene whose microstructure is intended to permit three-dimensional tissue penetration. The pin, however, has an inert character. The growth of tissue into or in contact with this body is therefore comparatively slow.